Hot-stage Polarizing Microscopy Research Articles

Exploring the phase behavior of C8-BTBT-C8 at ambient and high temperatures: insights and challenges from molecular dynamics simulations.

C8-BTBT-C8 is one promising candidate for the development of high-performance electronic devices based on thin-film technologies. Its monoclinic polymorph has a well-established role in thin-film growth. Yet, quite little information is available about its dynamics on the molecular scale, and the structures of the mesophases which form at high temperature (about 100 K above ambient temperature). The present study is devoted to the analysis of such phases, with the ultimate goal of developing molecular models. Already at ambient temperature, our molecular dynamics simulations reveal a rich conformational behavior of the alkyl side chains, with gauche conformations as leading structural defects. Heating promotes the formation of a stacking faulted mesophase (380 K), and a smectic phase, at 385 K, upon side chain melting. Although more disordered, this phase bears several analogies with the smectic A phase, experimentally observed at 382.5 K. At higher temperatures, the increase in configurational disorder is brought by molecular diffusion and other phenomena, finally leading to an isotropic molten phase. Our in-depth analysis, complemented by hot-stage polarizing microscopy data, provides interesting insights into this material, highlighting the challenges associated with the modeling of soft semiconducting systems.

Utilizing hot-stage polarized microscopy and ATR-FTIR for ramipril co-crystal screening, supported by principal component analysis and cluster analysis

Context: Co-crystal formation, a method for enhancing the physicochemical properties of active pharmaceutical ingredients (APIs), has gained traction in pharmaceutical research. However, the current landscape lacks comprehensive and dependable co-crystal screening methods. Aims: To implement and assess a comprehensive methodology for co-crystal screening. This methodology combines hot-stage polarized microscopy (HSPM) and attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy, along with principal component analysis (PCA) and cluster analysis (CA). Methods: Three binary compounds containing ramipril, an API that had not previously been co-crystallized, and three pharmaceutical coformers were investigated. The Kofler mixed fusion method was initially employed for initial co-crystal system identification. Subsequently, potential co-crystals were produced in a solid state via a procedure involving the gradual evaporation of the solvent. PCA and CA were applied to ATR-FTIR spectral data to identify patterns indicative of co-crystal formation. Results: Our analysis revealed characteristic ATR-FTIR bands indicative of the formation of hydrogen bonds between ramipril and its coformers, signifying the successful formation of co-crystals. Differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) measurements confirmed these findings. Experiments revealed two potential co-crystals, ramipril-vanillin, and ramipril-anthranilic acid. The study discusses the intricate HSPM images, spectra, thermogram of DSC, and X-ray diffraction properties of these systems in depth. Conclusions: Our findings validate the proposed methodology as a prospective tool for co-crystal screening, as ramipril co-crystals were successfully identified and characterized. This integrated method simplifies co-crystal screening and has the potential to substantially advance pharmaceutical research.

Partially hydrolyzed polyvinyl alcohol for fusion-based pharmaceutical formulation processes: Evaluation of suitable plasticizers.

The present study evaluates the effect of several pharmaceutical plasticizers on the thermo-physical and physicochemical properties of partially hydrolyzed poly(vinyl alcohol) (PVA) used in fusion-based pharmaceutical formulation processes. Specifically, the effect of mannitol (MAN), sorbitol (SOR), sucrose (SUC), anhydrous citric acid (CA), triethyl citrate (TEC) and low-molecular weight polyethylene glycol (PEG400) on PVA's melting properties, physical state and thermal degradation was evaluated via differential scanning calorimetry (DSC), powder X-ray diffractometry (pXRD) and thermo-gravimetric analysis (TGA). Results showed that the use of MAN, SOR, SUC and PEG400 led to the reduction of PVA's melting onset temperature, while MAN, SUC, CA and SOR were amorphously dispersed within PVA's matrix, and the addition of SUC and CA resulted in significant reduction of PVA's crystallinity. TGA results showed the formation of thermally highly unstable PVA mixtures in the cases of CA and TEC (degradation started from ~150°C and ~125°C, respectively), while significant molecular interactions were identified by FTIR in the cases of PVA-MAN, PVA-SOR and PVA-SUC. Hot-stage polarized microscopy (HSM) revealed PVA's melt miscibility only with MAN and SOR, while melt flow index (MFI) measurements showed that the use of MAN, SOR and PEG400 resulted in a significant improvement of PVA's melt flow properties. Finally, MD simulations were in close agreement with the experimental observations, indicating that they can be considered as a promising tool for the theoretical modelling of such systems.

Homocrystallization and Stereocomplex Crystallization Behaviors of As-Spun and Hot-Drawn Poly(l-lactide)/Poly(d-lactide) Blended Fibers During Heating.

A series of poly(l-lactide)/poly(d-lactide) blended chips (LDC), as-spun LD fibers (LDA) and hot-drawn LD fibers (LDH) were prepared for investigating the homocrystallization and stereocomplex crystallization behaviors of LDA and LDH fibers during heating. Modulated differential scanning calorimetry (MDSC), hot stage polarized microscopy (HSPM), and real-time wide-angle X-ray diffraction (WAXD) were used for studying the crystallization and melting behaviors, fiber morphology, and crystalline structure evolution of the LDA and LDH fibers’ homocrystals and stereocomplex crystals during heating. The molecular chain orientations of the LDA and LDH fibers were obtained through spinning and improved through the hot drawing processes. When the molecular chain was oriented on the fiber axis, the homocrystals and stereocomplex crystals of the fibers began to form in turn as the heating temperature exceeded the glass transition temperature of the fiber. The side-by-side packing of the molecular chains was promoted by mixing the molecular chains with the extrusion screw during the spinning process, facilitating stereocomplex crystallization. When the LDA fiber was heated above the glass transition temperature of the fiber, movement of the fiber molecular chain—including molecular chain orientation and relaxation, as well as crystallization, melting, and recrystallization of homocrystals and stereocomplex crystals—were investigated through HSPM. MDSC and real-time WAXD were used to observe the molecular chains of the melted poly(l-lactide) and poly(d-lactide) homocrystals of the fibers rearranging and transiting to form stereocomplex crystals during heating.

Physicochemical and mechanical properties of paracetamol cocrystal with 5-nitroisophthalic acid

We report novel pharmaceutical cocrystal of a popular antipyretic drug paracetamol (PCA) with coformer 5-nitroisophhthalic acid (5NIP) to improve its tabletability. The cocrystal (PCA-5NIP at molar ratio of 1:1) was synthesized by solvent evaporation technique using methanol as solvent. The physicochemical properties of cocrystal were characterized by powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), fourier transform infrared spectroscopy (FTIR), hot stage polarized microscopy (HSPM) and scanning electron microscopy (SEM). Stability of the cocrystal was assessed by storing them at 40°C/75% RH for one month. Compared to PCA, the cocrystal displayed superior tableting performance. PCA-5NIP cocrystal showed a similar dissolution profile as compared to PCA and exhibited good stability. This study showed the utility of PCA-5NIP cocrystal for improving mechanical properties of PCA.

Infrared Spectral Characteristics of Azobenzene Containing Side-Chain Liquid Crystal Polymer

In order to study the infrared spectral characteristics of side-chain liquid crystal polymer, an infrared monomer containing a permanent dipole azobenzene group spaced from the methacryloyl moiety by a polymethylene segment was synthesized in three steps starting from 4-cyanoaniline. The monomer was polymerized with a push-pull azobenzene monomer, (-)-menthy1 methacrylate in the presence of azobisisobutyronitrile (AIBN) as the radical initiator. Structurally similar amphiphilic polymers were obtained by polymerization of analogous methacrylates in which the polymethylene spacers was replaced by oligo (oxyethy1ene) segments. The obtained polymer was characterized by Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectro photometry (UV-vis), Hot Stage Polarized Microscopy (HS-POM), Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analyzer (TGA). Its infrared emissivity at different temperatures was tested by Bruker-V70 infrared analyzer. The results showed that the azobenzene poly (methyl methacrylate) (azo-PMMA) has high glass transition temperature(about 40°C), good thermal stability(divied in 294°C) and low infrared emission under 70%.

Feather‐like morphology of poly(methyl methacrylate)/poly(ethylene oxide) blends: The effect of cooling rate and poly(methyl methacrylate) content

ABSTRACTThe effect of cooling rate on the crystallization morphology and growth rate of poly(ethylene oxide) (PEO) and PEO/poly(methyl methacrylate) (PMMA) blends has been observed by Hot Stage Polarized Microscopy (HS‐POM). The isothermal crystallization kinetics study was carried out by differential scanning calorimetry (DSC). The spherulite morphology has been observed for the neat PEO with molecular weight of 6000 g/mol. By adding of PMMA with molecular weight of 39,300 g/mol, the growth fronts become irregular. With the increasing of PMMA content, the irregularity of growth front becomes more obvious, and the feather‐like morphology can be observed. When PMMA content is 60%, the spherulite is seriously destroyed. This phenomenon is more obvious for the slow cooling process. Based on the measurement of spherulite, the growth rate curves were obtained. According to the curves, it can be seen that the growth rate decreases with the increasing of PMMA content, and the growth rate during the slow cooling process is higher than that of the fast cooling process. The isothermal crystallization experiment indicates that the crystallization rate decreases dramatically with the increasing of PMMA content. And the Avrami parameter n was obtained, which is non‐integral and less than 3. Finally, it can be concluded that the higher value of n can be obtained for the condition with low crystallization rate. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41705.

High-temperature phase transformation and topochemical nature in ferroelastic (NH4)2SO4

The electrical conductivity of ferroelastic ammonium sulfate (NH4)2SO4 revealed an anomaly at around 130°C (=403K, TP) on heating with large and irreversible thermal hysteresis through thermal cycle. Ferroelastic domain walls and surface morphology of (NH4)2SO4 were investigated by hot-stage polarizing microscopy. Structural phase transition from an orthorhombic ferroelastic phase to a hexagonal paraelastic phase was not identified at TP upon heating. On further heating above TP, microscopic spots appeared and grew on the crystal surface, suggesting that the high-temperature anomaly at TP was an indication of an onset of thermal decomposition controlled by topochemical factors. The increase of electrical conductivity above TP was attributed to proton migration.

The influence of spiral jet-milling on the physicochemical properties of carbamazepine form III crystals: Quality by design approach

The purpose of this study was to investigate the influence of spiral jet-milling process on the physicochemical characteristics of α polymorphic active pharmaceutical ingredient, using Carbamazepine form III as a model drug, and taking into consideration Quality by Design (QbD) approach to pharmaceutical development. A 2(4-1) factorial screening design was implemented to identify the spiral jet-milling process variables that significantly affect the particle size distribution of milled samples. Diameter of injector nozzles, diameter of ring nozzles and air pressure were selected for further analysis using a 2(3-1) factorial experimental design. Particle size distribution of additional samples was determined, while physicochemical properties were examined by differential scanning calorimetry (DSC), hot-stage polarized microscopy (HSPM), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and compared to those of un-milled drug. The gathered results shown that applied experimental design approach is capable to predict material behavior and could help in better understanding of material behavior during jet-milling process. Created design space (DS) provides assurance of product quality, expressed as the powder particle sizes lower than 5μm, as well as, in initial polymorph form existence after jet-milling through combination and interaction of input variables.

Thermal analysis of binary liquid crystals eutectic system cholesteril p-phenoxi phenyl carbamate–cholesteril p-biphenyl carbamate

For a binary mixture of two liquid crystals, cholesteril p-phenoxi phenyl carbamate and cholesteril p- biphenyl carbamate, the solidus-liquidus equilibrium was investigated using differential scanning calorimetry (DSC) and the thermodynamic parameters were obtained. Simple eutectic point was observed for this system, situated approximately at the same temperature for all the studied compositions. This behavior is favored by grinding and is more evident in the composition 50:50. The excess func- tions G E and S E for the pre-, post-, and eutectic composi- tion have been calculated using the phase diagram data. Comparing the experimental data with the existing theo- retical data, the system deviation from the ideal behavior is observed. The structure of pure compounds was elucidated using FT-IR and hot-stage polarizing microscopy.

Crystallization Pathways and Kinetics of Carbamazepine–Nicotinamide Cocrystals from the Amorphous State by In Situ Thermomicroscopy, Spectroscopy, and Calorimetry Studies

The work presented here was motivated by the premise that the amorphous state serves as a medium to study cocrystal formation. The molecular mobility inherent to amorphous phases can lead to molecular associations between different components such that a single crystalline phase of multiple components or cocrystal is formed. Cocrystallization pathways and kinetics were investigated from amorphous equimolar phases of carbamazepine and nicotinamide using hot-stage polarized microscopy (HSPM), hot-stage Raman microscopy (HSRM), differential scanning calorimetry (DSC), and X-ray powder diffraction (XRPD). Nonisothermal studies revealed that amorphous phases generate cocrystals and that thermal history affects crystallization pathways in significant ways. Two different pathways to cocrystal formation from the amorphous phase were identified: (1) at low heating rates (3 degrees C/min) a metastable cocrystalline phase initially nucleates and transforms to the more stable cocrystalline phase of CBZ-NCT, and (2) at higher heating rates (10 degrees C/min) individual components crystallize, then melt and the stable cocrystalline phase nucleates and grows from the melt. Isothermal studies above the T(g) of the amorphous equimolar phase also confirm the nucleation of a metastable cocrystalline phase from the amorphous state followed by a solid phase mediated transformation to the stable cocrystalline phase. Cocrystallization kinetics were measured by image analysis and by thermal analysis from small samples and are described by the Avrami-Erofeev model. These findings have important implications for the use of amorphous phases in the discovery of cocrystals and to determine the propensity of cocrystallization from process-induced amorphization.

Preparation and evaluation of diltiazem hydrochloride-gelucire 43/01 floating granules prepared by melt granulation

The basic objective of this study was to explore the application of Gelucire 43/01 for the design of multi-unit floating systems of a highly water-soluble drug diltiazem HCl. Diltiazem HCl-Gelucire 43/01 granules were prepared by melt granulation technique. The granules were evaluated for in vitro and in vivo floating ability, surface topography, and in vitro drug release. Aging effect on storage was evaluated using scanning electron microscopy, hot stage polarizing microscopy (HSPM), differential scanning calorimetry (DSC), and in vitro drug release. Granules were retained in stomach at least for 6 hours. Approximately 65% to 80% drug was released over 6 hours with initial fast release from the surface. Surface topography, HSPM, DSC study of the aged samples showed phase transformation of Gelucire. The phase transformation also caused significant increase in drug release. In conclusion, hydrophobic lipid, Gelucire 43/01, can be considered as an effective carrier for design of a multi-unit floating drug delivery system of highly water-soluble drugs such as diltiazem HCl.

Phase Diagram, Caesium-133 NMR Spectra and Electrical Conductivity of the Binary System Caesium and Zinc Butyrates

Abstract Phase equilibria of non-mesogenic caesium- and zinc-butyrate mixtures were studied by differential thermal analysis and hot stage polarization microscopy. Smectic liquid crystals were found in some composition range. Their appearance is explained by the latent mesomorphism of caesium butyrate. |133Cs NMR spectra and the specific electrical conductivity of the molten mixtures at 155°C were employed to investigate the peculiarities of ionic association and interaction in the melts.

Liquid Crystals in Binary Systems of Lead Decanoate with Zinc or Cadmium Decanoate

Abstract The phase transition temperatures were determined by differential thermal analysis and hot stage polarization microscopy between room temperature and the isotropic liquid region for the binary systems of lead (II) decanoate with zinc (II) or cadmium (II) decanoate. The boundaries of the liquid crystal formation in these systems were found.

Mesophase and Glass Formation in Binary Systems of Caesium and Alkali-Earth Metal Butyrates

Abstract The phase diagrams of the binary systems of non-mesomorphic components such as caesium-mag-nesium, caesium-calcium and caesium-barium butyrates have been studied by differential thermal analysis and hot stage polarization microscopy. Smectic liquid crystals are found in some composition ranges of the binaries with calcium and barium butyrates. The liquid crystal appearance in these systems is explained by the exhibition of latent mesomorphism of caesium butyrate. Glasses are obtained in all systems studied, the formation of vitreous optical anisotropic mesophase being revealed only for binary from caesium and barium butyrates.

Synthesis and properties of some new pyridinium salt models and polymers

Two monomers, 1,4-bis(4-pyridyl) and 1,4-bis(3-pyridyl) azines were synthesized and characterized. Model pyridinium salts were synthesized by condensation of azines with some bromoalkanes. Polymerization of azines with some dibromoalkanes was also carried out to form pyridinium salt polymers. The structures of both model compounds and polymers were verified from their elemental analysis, IR and 1H NMR spectra. The liquid crystalline properties of models and polymers were studied by differential scanning calorimetry (DSC) and hot-stage polarizing microscopy. These studies revealed that some synthesized model compounds and polymers exhibit nematic liquid crystal texture having low thermal liquid crystalline stability. The terminal alkyl chains were found to produce mild effect of lowering the transition temperatures. Viscosity measurements indicate that the synthesized polymers have low molecular weight.

Synthesis and mesomorphic properties of some biphenyl-phenyl triesters as potential longitudinal ferroelectrics

Abstract A homologous series of “fraternal twin” molecules consisting of relatively short and relatively long mesogenic units connected by a flexible spacer group and flexible chains as the terminal groups was synthesized in an attempt to form a non-chiral longitudinal ferroelectric smectic phase. The shorter of the two mesogenic units consisted of a 4-alkyl/alkoxy substituted biphenyl ester; the longer a terbenzoate group. Mesomorphic properties were determined by hot-stage polarizing microscopy and DSC. Several smectic phases were observed as well as nematic phases. Characterization of the smectic phases by microscopic textures is discussed.

Phase Diagrams of Binary Alkanoate Systems with Common Cation: Potassium Isobutyrate-Propionate, and Sodium Butyrate-Isobutyrate

Abstract The phase diagrams of the binary mixtures of mesogenic potassium isobutyrate with non-mesogenic potassium propionate and mesogenic sodium butyrate with non-mesogenic sodium isobutyrate have been investigated by differential thermal analysis and hot stage polarization microscopy. Both systems have one eutectic and one metatectic phase equilibriums. Pecularities of liquid crystal formation in binary alkanoate systems with common alkali metal cation are discussed and compared with those of systems with common anion.

Liquid Crystals and Glasses in Binary Systems from Sodium and Alkali-Earth Metal Butyrates

Abstract The temperature and composition ranges of liquid crystal and glass formation have been established for the binary mixtures of mesogenic sodium butyrate with non-mesogenic magnesium, calcium and strontium butyrates by means of differential thermal analysis and hot stage polarization microscopy. The formation of a vitreous optically anisotropic mesophase has been found for binaries of sodium butyrate with calcium and strontium butyrates.

Phase Diagram of the Binary System of Barium and Sodium n-Butanoates

The phase diagram of the binary system of barium and sodium n-butanoates has been studied by differential thermal analysis, hot stage polarization microscopy, and small angle X-ray diffraction. Pur...